1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to dampening mechanisms for electrical switching apparatus, such as draw-out circuit breakers.
2. Background Information
Electrical switching apparatus used in power distribution systems are often mounted within a switchgear enclosure either individually or in combination with other switchgear (e.g., without limitation, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers).
Some electrical switching apparatus such as, for example, some medium-voltage and low-voltage circuit breakers, can be relatively large. In order to facilitate movement (e.g., installation; removal; maintenance), some circuit breakers are commonly coupled to draw-out mechanisms which permit such circuit breakers to be drawn out of the switchgear enclosure. Accordingly, such circuit breakers are commonly known in the art as “draw-out” circuit breakers. The circuit breaker may be further supported within a draw-out frame, commonly known in the art as a cassette or chassis. The switchgear enclosure generally includes a number of cells, with each cell being structured to receive a corresponding circuit breaker. The draw-out mechanism includes, for example, a combination of rails and rollers coupled to one or the other, or both, of the sidewalls of the cell and the sides of the corresponding circuit breaker, which is to be drawn into and out of the cell. Draw-out circuit breakers are described in further detail, for example, in commonly assigned U.S. Pat. No. 7,019,229, which is hereby incorporated herein by reference.
Under certain circumstances such as, for example, when the circuit breaker trips in response to an electrical fault condition (e.g., without limitation, a current overload; a short circuit; an abnormal voltage or some other fault condition), the circuit breaker may be subjected to relatively large magnetic repulsion forces. Such forces have a tendency to induce impulse type motion resulting in undesirable vertical movement of the circuit breaker within the cell of the switchgear enclosure.
One prior proposal for resisting such movement includes an arrangement of manually adjusted hardware such as, for example, a plurality of bolts which are tightened or loosened until they suitably engage a corresponding feature (e.g., without limitation, a bracket; a shelf; a ledge; a protrusion) of the switchgear enclosure. Another prior proposal which is disclosed in commonly assigned U.S. Pat. No. 7,486,499, which is incorporated herein by reference, incorporates a securing mechanism having a conglomeration of movable engagement members (e.g., steel bars) and springs mounted to the circuit breaker and designed to automatically adjust and securely engage the switchgear enclosure as the circuit breaker is moved into the fully installed position. However, each of the foregoing approaches suffers from its own unique set of disadvantages.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in dampening mechanisms therefor.